The goal of this project is to define the molecular mechanism by which androgenic steroid withdrawal initiates the onset of a programmed death known as "apoptosis" in mammalian prostate cells. Currently it is our ability to access this process that provides our main weapon in the fight against prostate cancer. Apoptosis is a genetically-active cell process and requires the prostate cell to synthesize new substances in order to die. Recently, we have obtained evidence that implies that apoptosis occurs when the differentiated prostate cell attempts to proliferate but is unable to complete this process. This hypothesis opens new opportunities for our ability to dissect the molecular mechanism of apoptosis because it implies that some cytokine stimulus must be initiating this process and that the intracellular signaling systems participate in driving the cell to its death. With the intent of better defining the apoptotic stimulus and dissecting the cellular signaling systems involved in apoptosis, the specific aims of the next years of this proposal will be: 1.To characterize the growth factor and cytokine environment of the rat ventral prostate gland during the acute (first 5 days) period following androgen withdrawal. Quantitative RNA-PCR based assays in addition to ribonuclease protection assays and immunochemical procedures will be used to survey the presence of numerous growth factor and cytokine substances during prostatic regression. 2.Involvement of the intracellular second messenger systems in initiating the apoptotic response will be investigated by quantitating changes in the intra-cellular concentrations of cyclic nucleotides during early regression. In addition we will purify and sequence proteins that become tyrosine-phosphorylated rapidly after castration in an attempt to establish whether they are receptors for an apoptotic cytokine substance or whether they mediate the intracellular response for apoptosis by carrying the signal to the nucleus. 3.We will utilize a well-defined prostate explant culture system to identify agents that can modify the ability of rat prostate cells to undergo apoptosis. Ventral prostate cells grown in testosterone-free medium rapidly begin to enter apoptosis. By supplementing back various kinase stimulators/inhibitors and growth factor/cytokines, we can test the role of these factors and cell modifiers.